AS2 (and AS1) were never really meant to be a programming language, just a light scripting language for helping do dynamic things in animation. They were really never intended for games. They are missing a lot of features and constructs that belong to a normal programming language and have slightly unusual syntax.

AS3 is the reworking of AS2, but it's been built into a rather powerful and much more feature complete programming language, with various advanced features like classes, inheritance, strict data typing, etc.

If you're looking for syntactical differences, there are way to many to list. The two are about as closely related as Javascript to C++.

zot
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2011-10-25T15:32:49Z —
#3

Javascript to C++ is a good analogy. If you're looking to do some basic animation with flash, AS2 is good enough. If you're making a game or an application, then AS3.